Production of images



Jan. 10, 1939. P. SELENYI PRODUCTION OF IMAGES Filed March 20, 1935 2 Sheets-Sheet l M illllllmulilil will"hmllnmlImfl P. SELENYI Jan. 10, 1939.

PRODUCT ION OF IMAGES Filed March 20, 1935 2 Sheets-Sheet 2 INVENTOR- ATTORNEY- Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE PRODUCTION OF WAGES Application March 20, 1935, Serial no. 12,038 In Hungary March 22, 1934 12 Claims. (Cl. 178-73) This invention relates to production of images;

and it comprises a process of and apparatus for producing images or pictures by means of a beam of gaseous ions produced at gas pressures varying from a few thousandths of a millimeter of mercury to about atmospheric pressure, the said beam oi ions being controlled in predetermined manner as to intensity, and usually in accordance with point to point diflerences in density 10 or depth of shading 01 an image to be reproduced, and then projected against an insulating screen, the beam 01' ions and the screen being maintained in relative motion and the screen being advantageously in the form of an endless ll band, thereby producing a latent electrical image which is capable of development by dusting the same with suitable powders and which after development may be fixed if desired; all as more fully hereinafter set forth and as claimed.

20 In the specification of my U. S. A. Patent No.

1,818,760 I have described a cathode-ray oscillograph, which has no fluorescent screen, but writes its record on the inner glass wall of the tube by means of a negatively charged pencil" 25 of rays in the shape of a permanent but invisible line drawn with electrical charges, which can be made visible by spraying the outer wall with a suitable powder. For some purposes this device has important advantages over other in- 30 struments which rely upon the motion of mechanical elements to detect or indicate variations in such conditions as the intensity of light or of an E. M. F. for example. The response of the cathode ray to a change of condition is ins tan- 5 taneous; it has no detectable inertia. Methods have also been proposed for use of this cathode ray tube for recording as well as indicating variations in the character or intensity of a condition but these'methods have not progressed beyond 40 the stage of laboratory curiosities owing to certain inherent limitations in the use of the cathode ray.

Chief among the limitations of this cathode ray oscillograph is the requirement for an ex- 1 5 tremely high vacuum.

Any residual gas in the cathode tube produces gaseous ions which definitely interfere with the method. These ions neutralize the electric charges produced by the beam of cathode rays.

50 And to hold the vacuum sufilciently low to eliminate these ions is extremely diflicult.

I have found surprisingly that gaseous ions themselves, heretofore always considered'detrimental, can be employed as a means for making reproductions or records ot the variations o! a condition. A beam of such ions is relatively easy to produce and a high vacuum is not required. In fact it is necessary to employ a gas pressure above any employed in the cathode ray tube in order to produce a suilicient quantity of 5 these ions. 1 have found that the gas pressure can be varied all the way from about 0.001 mm. 01' mercury to atmospheric pressures or even slightly above. Higher pressures are not as advantageous.

It has been found relatively simple, for example, to obtain a beam of gaseous ions having like charges and substantially free from oppositely charged particles. It is also possible to employ much lower voltages than those used in the oper-. l5 ation of cathode ray tubes. A lower consumption is obtained. But none of the advantages of instantaneous response to a change of condition, etc. are sacrificed.

In carrying out my invention for recording the variations of a condition, for example, it is merely necessary to transform the instantaneous relative values of the condition into corresponding values of an E. M. F. or of a magnetic field and to apply the latter values to a beam of gaseous ions in such manner as to vary the intensity of such beam. This beam of ions may then be utilized for the production of a latent image in substantially the same manner as the cathode .ray is utilized in the mentioned oscillograph, ex-

cept for the fact that the higher gas pressures employed in my method eliminates most of the diiiiculties involved in the use of the cathode ray. The latent image can be developed and fixed by methods very similar to those employed in making the mentioned cathode ray oscillograms.

In the following description I have applied the name electrography to the art of utilizing a beam of gaseous ions for making records as in my invention and the records obtained I have called e1ectrograms".

My invention comprises broadly the use of a beam of gaseous ions to detect, indicate or reproduce variations of any condition, the variations of which are or can be translated into changes in E. M. F. or magnetic force. This invention is obviously capable of the most widespread uses which range all the Way from the simple measurement of an electric current to the reproduction of sounds and even to television. 5 These various uses will be evident to those skilled in the art from the following description of certain illustrative embodiments of the invention.

The apparatus of my invention comprises the various elements necessary-for carrying out the described process. This apparatus always includes a source of gaseous ions, an electrode or plate for attracting a beam of the said ions, an insulating body having advantageously the shape of a sheet, a membrane, or a ribbon, which affords a receiving surface capable of storing the efiects of the ion charges and which is arranged to intersect the path of the beam of ions, and mechanical means for producing relative motion of the beam of ions and of the receiving surface. The apparatus also may include means for transforming the condition to be measured or recorded into corresponding values of E. M. F. or of magnetic force, and for applying the latter to the beam of ions in such manner as to vary its intensity in accordance with variations in the condition.

The apparatus in certain of its modifications includes means for controlling the beam of ions, the varying control arrangement being usually operatively connected to this means.

The accompanying drawings show more or less diagrammatically various assemblages of apparatus elements within the scope of my invention and useful in conducting the process thereof.

In this showing:

Fig. 1 illustrates an apparatus which may be of electrography;

Fig. 2 shows an electrogram obtained with the ap aratus of Fig. 1;

Fig. 3 represents an improved apparatus in which a control electrode or grid is employed;

Fig. 4 shows an electrogram obtained with the ap aratus of Fig. 3;

Fig. 5 shows the diagram of an alternating current vol a e connected in series with a direct current vo tage:

Fi 6 illustrates an apparatus suitable for taking sound records. for example, by electrography; Figs. '7 and 8 represent sound electrograms taken with the aid of the apparatus of Fig. 6, while Fig. 9 represents a television receiving appara tus.

In the various figures like elements are desighated b like re erence numerals. Referring to Fi 1. element 5 is a carbon electrode serving to form an el ctr c arc with another similar electrode: these elect odes being connected in series with the battery 2 and a resistance 3. Opposite the are there is mounted. at a distance of a few mi l meters, a thin insulating sheet 9 of hard rubber. for examp e, having a thickness of say 0.2 to 1 mm. This is mounted on a sheet of metal 5 which forms the plate or electrode which serves to attract a beam of gaseous ions from the arc. The late and insulating sheet which forms the receiving surface are mounted in such manner that they may be moved at various speeds in the direction of the arrow i in front of the arc. The plate 5 is connected to a source 7 of alternating current of which an electrogram is to be taken; the other terminal of the alternating current being connected to one terminal of the battery 2.

In the operation of the device of Fig. 1, the electric arc generates gaseous ions part of which are negatively and part positively charged. During one-half cycle of the alternating current the plate 5 is evidently charged negatively with respect to the electric arc and at this moment the plate attracts positively charged ions which are intercepted by the screen 6 and held on the screen by electrostatic forces; the plate 5 and screen 6 acting as one plate and the dielectric, respectively, of an electric condenser. During this part of the cycle the plate and screen are moved through a predetermined distance, hence there is producedon the screen a spot of positive ions having a shape resembling the arc .with a width depending upon the rapidity of motion of the plate and screen. During the next succeeding part of the electric cycle the plate is charged positively with respect to the arc and hence a beam of negatively charged ions is attracted to the plate 5. This beam is again intercepted by the screen, the ion charges being held on the screen as before and a spot of negatively charged ions being produced. This latter spot is produced at some distance to one side of the first spot of positively charged ions owing to the motion of the plate and screen. It is thus seen that a latent image is produced on the screen comprising a row or series of spots of ions being charged alternately positively and negatively.

The latent image on the screen 6 can be developed by any of the methods used in the development of cathode ray oscillograms mentioned above. For eXa ple the screen may be sprayed by a mixture of nely powdered sulfur and minium, the well-known ele'ctroscopic powder. In

c this powder the sulfur is charged negatively and used in the demonstration of the phenomenon the red lead positively, hence particles of sulfur Will become attached to the screen wherever there is a collection of positive ions and the red lead will become deposited upon the negatively charged spots. The result produced is shown in Fig. 2.

In Fig. 2 the spots marked A are red, since covered with Ininiuin, while the spots marked B are yellow 'due to the sulfur present. Thus a picture or record of the alternating current is produced; a record from which the frequency can be detemined provided the speed of the screen is known. It is also possible to gain a rough measure of the relative voltages of several sources of E. M. F. by this method, the voltages being estimated from the amount of sulfur and minium retained on the screen. And of course a pulsating current can be distinguished from an alternating current, etc. The record obtained from the simple apparatus shown in Fig. 1, therefore gives a surprisingly large amount of information.

A record produced as described above can be projected on a screen by a stereopticon without being fixed. The record can, however, be readily fixed by spraying with a transparent binder such as shellac or a nitrocellulose lacquer, for example. Instead of fixing, the sulfur and miniu'm, held to the screen only by electrostatic forces, can be removed by wiping; the electrical charges can be dissipated by heating or by other methods and the screen is then ready for further use.

A considerably moreperfect record can be obtained by use of the equipment shown in Fig. 3. In this figure element l, as before, represents one of two electrodes serving to form an electric arc, these electrodes being connected in series to the battery 2 and resistance 3. In this figure the two electrodes are arranged so as to spread out the arc to some extent in front of the screen 6. In between the screen 6 and the are there is interposed a diaphragm 8 provided with a narrow slit 9, directly opposite the arc. This slit produces a narrow beam of ions, excluding the rest. It may have a width ranging from a few hundredths to a few tenths of a millimeter. The beam of ions passing through this slit falls on the screen 6 in the form of a line of definite length and width.

When a source of alternating current I is connected between the plate 5 and the arc a record is obtained similar to that shown in Fig. 4, the record being in the form 01 bands alternating in sign of electric charge. This record is very similar to the so-called "sound tracks of variable density" obtained in sound film technique. And in fact if a variable condition is utilized, for example if the voltage between the plate and the arc is made to vary with sound, the record obtained can be considered a picture or record of the sound. The production of such records will be explained more fully below.

It will be noted that the record shown in Fig. 4 does not quite represent a true picture or record of the alternating current. For example the distance between the various bands is of finite width, while it is known that the voltage of the alternating current merely passes through a value of zero. This is explained by the fact that a certain definite voltage, 1. e., a certain electrostatic charge, is required to make the powder particles adhere to the insulating surface, i. e., the hard rubber sheet. Whenever the charge of this surface is less than this particular value, no powder will adhere. It is possible to obtain a more accurate representation of the alternating current by imposing a bias voltage upon the alternating current.

In Fig. 5 there is shown a representation of an alternating current of voltage E connected in series with a bias direct current voltage U. If such a system is connected between the plate 5 and the arc of Fig. 3, as at I, and if the value of the bias voltage is correctly chosen a more accurate representation of the alternating current or other variable condition will be obtained. The best record is obtained of an alternating current when the bias voltage exceeds the maximum voltage of the alternating current voltage by an amount just suflicient to attract ions to the plate 5 when the two voltages are in opposite sense. The record will then not completely fade out at any point but the charges produced on the screen will all be of the same sign. The quantity of electroscopic powder retained on the screen at any point indicates the magnitude of the corresponding voltage. An undistorted representation will also be obtained provided a bias voltage greater than that indicated is employed but in this case the ground will be covered throughout by developing powder.

The employment of a bias voltage has another advantage. When the voltage between the arc and the plate is low, approaching zero, the speed of the ions in traversing the distance between the arc and the screen cannot be neglected. If the screen is moved rapidly, therefore there is a certain lag before the ions reach the screen and this causes a phase displacement. This is eliminated provided the bias voltage is chosen sufficiently high so that the variation in the speed of the ions becomes negligible.

For special purposes it is of course possible to employ alternating or other types of voltage for bias purposes as desired. It is also possible to avoid phase displacement provided a plate voltage is maintained at a sufficient value and provided the variable condition is applied to an intermediate control electrode or grid, as will be described later. In the embodiments so far described the variable condition is imposed in the plate voltage.

The device shown in Fig. 3 can be employed to produce the so-called sound tracks used in the motion picture industry by a very simple manipulation. Thus a sound may be received by one of the usual microphones, the electric currents thereby set up being amplified to suitable extent and this source of E. M. F. being applied as plate voltage or as grid voltage to the plate 5 or the diaphragm 8, respectively. Then, by displacing the plate 5 at uniform speed a record similar to that of Fig. 4 would be obtained as a record of a note of constant pitch, for example.

When the variable condition evidences itself in a varying plate voltage it is necessary that this voltage should have a magnitude of at least about 100 volts. If a grid or control electrode, such as the element 8 in Fig. 3 is employed, this voltage may be greatly reduced and a more fiexible and practical control obtained. When used as a grid control electrode, element 8 is made of metal. It may be a Wire screen or a plate provided with one or more slits. The varying controlling circuit is then connected to this element, the other terminal being usually connected to the source of ions. When such a grid is employed my device has all the characteristics of the three electrode vacuum tube and can be used in similar manner. Control of the intensity of the beam of ions is effected by means of the electric field set up by the grid. The source of ions acts as the filament or cathode and the plate 5 serves as the plate, as in a vacuum tube. My device operates withthe so-called space-charge current, that is, a current in which electric particles all having the same charge are moving from the source of ions to the plate, provided a bias plate voltage is employed of sufiicient magnitude to always maintain the plate charged with the same sign with respect to the source of ions. When a control electrode or grid is employed the amplification factor of my device is very large, that is, a large plate current can be controlled by means of a very low grid voltage.

In one specific embodiment of my invention I employed as a source of ions a heated strip of platinum, having the dimensions of 10 by 2 by 0.2 mm., coated with an alkaline earth metal oxide. The grid was a sheet of metal having a thickness of 0.5 mm. and was provided with a slit 5 by 0.5 mm. The screen was a sheet of hard rubber having a thickness of 0.25 mm. mounted on the external surface of a revolving metal cylinder the latter serving as the plate. The distance between the incandescent cathode and the receiving surface was 0.5 mm. An E. M. F. of 600 volts was connected across the plate and the incandescent cathode of this device and when an alternating current voltage of 0.4 volt was connected to the grid, a perfectly controlled record was obtained upon rotation of the cylinder; a record which, when developed with electroscopic powder, varied in depth (of minium) from zero to a considerable value. Since the maximum value of the alternating current voltage connected to the grid was about 0.6 volt, this result indicates an amplification factor of about 1000. In other cases even higher degrees of sensitivity have been obtained, grid voltages varying between 0.05 to 0.1 volt being sufficient to produce appreciable changes of intensity upon the record.

The use of the three electrode embodiment of my device may be further illustrated by reference to the remaining figures of the drawings.

Fig. 6, for example, is a diagrammatic representation of an equipment suitable for producing the so-called sound tracks of a sound film or of the so-called film gramaphone. In this figure I0 represents the indirectly heated incandescent cathode functioning as a source of ions. This element may be for example a small tube of platinum coated with an alkaline earth oxide. The heater of the cathodeis a small wire passing through the platinum tube and insulated therefrom by means of a layer of magnesia for example. The cathode is advantageously arranged at right angles to the motion of the film and parallel to the slit I2 in the grid or control electrode II. For convenience in illustration, however, the cathode of Fig. 6 has been shown perpendicular to the slit.

The heater of the cathode is energized by means of the electric circuit including the battery 2 and resistance 3. The slit I2 in the grid II is arranged at right angles to the plane of the drawing and to the motion of the film I3. The film is made of transparent insulating material, such as acetyl cellulose, and is used as a receiving surface, for the sound pictures. The unexposed film is reeled oil the spool I4 at a constant linear speed and is reeled up on the spool I4. The plate voltage is supplied by the battery 5|, the positive terminal of which is connected to a metal drum I5 and which serves as plate. The negative terminal of the plate battery 5| is connected to the incandescent cathode.

The reception of the sound in Fig. 6 is effected by the microphone I6, which is fed by current from battery H. The transmitting transformer is represented at I8. The sound current is amplified if necessary by means of the conventional amplifying equipment shown diagrammatically at IS. The amplified voltage is shown connected in series to a biasing potential supplied by the battery 20 and is then connected between the incandescent cathode II] and the grid II. It is, of course, possible to connect the sound voltage between the plate I5 and the grid II.

The film passes over the drum I5 in the direction indicated by the arrows and receives upon its surface a deposit of gaseous ions which thereby produce a latent image. This latent image is developed in the chamber 2 I where the film is sprayed by electrically charged powder particles projected by a blast of. air for example. Means for fixing the record is shown at 22 in the form of a spray gun for coating the film with a light film of lacquer for example. The solvent is evaporated from the lacquer prior to reeling up the film. If desired it is of course possible to optically project or to copy the image either before or after fixing and reeling.

It is believed that it would be obvious to those skilled in the art from the description already given how the method of my invention can be adapted to television, for example. However, for the sake of completeness, an illustrative embodiment of a device suitable for use as a television receiving set has been shown in Fig. 9. In this device it is advantageous to employ a so-called Nipkow disc, which is shown at I I, this disc acting to some extent like the grid II of. Fig. 6. The disc is provided with a series of Openings I2, which may be arranged in a spiral or more advantageously, as in the device illustrated, in a circle concentric with the axis of the disc. An endless insulating film I3 is employed in this embodiment, which is moved in the direction indicated by the arrows 28 by the rotation of reels I5 and I5. An endless band 29 is employed as a plate in this case, this band being driven by drums 30 and 30'. The band 29 is made of conducting material, usually of metal, and is mounted to pass in close proximity to the film I3. It is driven at the same speed as the film and in the same direction by suitable means not shown.

The receiving antenna is shown at 32. The electrical impulses received are amplified and usually rectified by the device shown diagrammatically at I 9. One terminal of the amplifier is connected through the bias E. M. F. 20 and the metal brush 35 to the metallic Nipkow disc II, while the other terminal is connected to the incandescent cathode III. The latter is heated indirectly by means of the source of current indicated at 25. The plate voltage is supplied by the battery 5|, which is connected to one of the pulleys 30, as well as to the cathode. Development of the latent images produced upon the film by the beam of ions is accomplished in the device shown diagrammatically at 2|, which is prov ded with a means 31 for the introduction of a blast of electroscopic powder of desired type.

As will be readily understood from the preceding discussion the film traveling in the direction of the arrows passes in front of. the cathode I0 and receives on its surface a beam of gaseous ions. The cathode is advantageously arranged transverse of the film, although for convenience of illustration it has been shown in Fig. 9 in a position parallel to the film. The operative length of the cathode corresponds to the distance between two of the perforations I2 of the Nipkow disc. The electric impulses received by the antenna vary the intensity of the beam of ions, these impulses being received by the Nipkow disc which acts in a manner similar to the grid of a three electrode vacuum tube. The rotation of the disc provides transverse motion of the beam of ions across the film to produce a line element of the desired picture while analysis in the direction of. the motion of the film is accomplished by the motion itself.

The Nipkow disc and the film are, of course, driven insynchronism with the picture analyzing elements of the transmitting station.

Fig. 9 discloses the combination of a wireless picture transmitter of a known kind in combination with an electrographic picture receiver according to the present invention. As shown in the drawings, the film II3, which moves with constant velocity in the direction of the arrow I28, carries the pictures to be transmitted. The film runs from the reel H4 onto the reel H4, being kept moving by the well known toothed cylinders H5, 5', which also keep the film under tension in a plane parallel to the Nipkow disc. This disc, which serves for analyzing the pictures into so-called picture points, is formed with a series of holes I I2 arranged concentrically to the centre of the disc. MI is a line-shaped source of light, which may be a strongly lighted slit, an incandescent lamp with a straight-line filament or the like. The longitudinal axis of the source of light extends in parallel to the plane of the film and vertically to the drawing. The lens I42 projects an image of the source of light onto the circle of holes in the Nipkow disc and the light traversing the holes is collected by the lens I43 and concentrated onto the photoelectric cell I44. The current in the circuit governed by this cell, which varies according to the intensity of. light at each individual movement, is amplified in the amplifier I45 and utilized in the known transmitting device I46 for modulating the high frequency oscillations. The radio waves modulated in this manner are emitted by the antenna I32 and received by the antenna 32 of the receiver. A transmitted potential corresponding to a dark spot on the picture beingtransmitted produces a voltage at the receiving station which, in conjunction with the bias E. M. F. 20, produces a corresponding intensity of the beam of gaseous ions passing through the corresponding perforation of the Nipkow disc ll. Thus the picture or image which is beingtransmitted is scanned in synchronism with the scanning produced by the Nipkow disc II and the motion of the film l3 at the receiving station of Fig. 9. The latent image produced upon the film thus corresponds to the picture or image which has been transmitted.

The latent image is developed in the device shown at 2| and then passes before the source of illumination 38 and the frosted glass plate 39. This developed image can be viewed directly by means of the rotating mirror 40 which is rotated in synchronism with the film, or it can be projected upon a screen by known methods. The image is removed from the film by the device shown at 4| which may be a rotating brush. The electrostatic charges produced on the film by removal of the electroscopic powder are removed by the heated cathode 24. This means for removing electrostatic charges can be replaced by various other devices such as a fiame oran arc, for example.

After the image is removed from the film as described, the film is then ready to receive another latent image. The process thus resembles to some extent that known as the intermediate film process of television, and it can be employed in a similar mannerat a considerable saving in cost both of equipment and operating expense.

One particular advantage which the described process has over the intermediate film process, at the receiving station, is that the varying conditions are used directly, applied to the grid, for

the making of the electrograms and it is not necessary to transform these varying conditions into corresponding fluctuations of light and to project the latter fluctuations upon a moving film. In this way it is possible to dispense with such devices as the Kerr cells, etc. used in the photographic process. For this reason it is sometimes of advantage to employ the electrographic method for the production of sound records even when the final record is to be obtained in photographic form. Thus the sound electrogram can be readily copied, after development upon the border of a sound film.

By the use of my device with control electrode or grid, as described in connection with Figs. 3, 8 and 9, it is possible in many cases to utilize the amplification of the device to dispense with the amplifying means usually employed in producing records of sound tracks, etc. Perfect sound records have been obtained for example by speaking into a microphone and connecting the secondary coil of the transmitter (a transformer with open iron core) across incandescent cathode and grid.

I have found that, after taking some of the peculiar characteristics of the device into account, all the rules known from radio technique in connection with electron tubes can be applied to this 3-electrode device. It possesses a grid voltageanode current characteristic similar to that of the three electrode vacuum tube or audion. It follows from this that it is not necessary that the control electrode should be situated between the source of ions and the plate, it being also possible for the grid to be arranged at any place in the vicinity of the source of ions from which place itis possible for it to exert its controlling action. By suitably altering the plate voltage and the grid potential it is possible to operate on the straight line part of the characteristic, whereby a record free from distortion can be obtained. It is also possible to operate on the lower bend of the characteristic and in this case the device will operate as a. rectifier. It is thus possible in the reception of sound pictures or of television. for example, to omit the detecting tube from the amplifying equipmentand to apply the modulated high frequency potentials directly to the grid. It is also possible to employ a plurality of control electrodes with different potentials applied to each, after the manner of multi-grid tubes. Feed back can also be employed. It is not necessary that the grid be perforated, since the desired effect can be obtained ior example with solid electrodes arranged in parallel to the beam of ions and forming its lateral boundaries.

The sensitivity of the electrographic process approaches that of the photographic process. Thus I have found that it is possible to draw an electrogram of about 15 square centimeters area within one second with a plate current of only amps, that is, with a total consumption of 10- coulombs. This sensitivity can be increased still further. The grid current usually has a magnitude of about 10 to 10" amps. The cost of operation is almost negligible. It is therefore obvious that the use of electrography has an important advantage over the use of photography in television. Another advantage of electrography over photography is that in the latter process the picture taken becomes visible only after a time lag of at least 20-30 seconds, while the development of an electrogram is completed within the fraction of a second.

The plate element employed in electrography does not need to be in actual contact with the insulating receiving surface. It may be spaced therefrom by from about 0.01 to 0.5 mm. On the other hand this plate does not necessarily have to be behind the film. In some cases, for example when a low gas pressure is used, it may be placed in front of the film, in which case perforations are provided for the transmission of the beam of ions. The composition of the plate may be varied widely. It is only necessary to employ a relatively good conductor to produce an equipotential surface. Or the insulating film may be mounted on a band of metal. It has been found that such a structure, if dusted on the receiving surface only, does not cause any diificulties in development even though the plate is connected to the plate voltage when passing through the development chamber. The plate may also consist of graphite or other conducting particles embedded in the back of the film. Or metal can be sputtered or cathodically dispersed upon the back of the film in such thin layers that the film is semi-transparent or translucent.

The electroscopic powder employed in the invention may be of widely different type. Besides the mixture of minium and sulfur mentioned previously it is also possible to employ a variety of other powders, especially if the electrograph consists of particles having charges of the same sign which is always the case when the bias tension is of sufficient magnitude.

It is evident that my method may be employed in an evacuated chamber as well as at atmospheric pressure. One advantage of employing reduced pressure is that it enlarges the range of choice for the source of ions. At lower pressures it is possible to employ the so-called glow discharge as a source of ions or a simple heated cathode may serve. At higher pressures it is possible to employ the so-called silent discharge produced on points of wires, etc. by the tension of a few thousand volts. Or when the open air is used an ordinary fiame may be used as source of ions. In general I prefer to employ a strip of metal heated indirectly and coated with electron emitting salts such as alkaline earth metal oxides. Cathodes of this nature have the advantage that they can be shaped into designs, for example, it is simple to produce a linear source of ions by the use of a small platinum tube coated with an alkaline earth metal oxide.

The entire apparatus shown in Fig. 6 and 9 may be surrounded by an evacuated chamber or only certain parts of these equipments. It is possible for example to make the electrograms in a reduced pressure but to develop and project them at atmospheric pressures. To accomplish this it is only necessary to provide long restricted passages through which to pass the film, which passages produce a high resistance to flow of gases into the evacuated space. It is necessary, of course, to provide continuous evacuation of the chamber in which a reduced pressure is maintained.

In making electrograms it is possible to move I (1) the receiving surface and plate (2) the source of ions and the grid, if a grid is employed or (3) the grid alone, in order to obtain the desired record. The first two embodiments are clear from the foregoing description. In order to produce an equipment in which a moving grid alone is employed it is possible, for example, to employ an arc with electrodes in axial alignment and a cylindrical grid or diaphragm surrounding the are having a concentric axis and capable of rotation about the common axis. The receiving surface in this case is mounted on the inside of another cylinder which is also mounted concentrically but which does not rotate during the taking of the electrograms. It is always necessary, of course, to have the receiving surface, the source of ions and the grid spaced, at fixed distances provided phase displacement is to be avoided.

The electrographio process can be used with advantage for printing, 1. e., for the production of positive paper prints of film negatives and also for making photographic enlargements. This can be effected in the way hereinafter described for the transmission of pictures, however in that case the transmitter and the receiver are combined. mechanically into a self-contained unit.

Electrography can be employed advantageously in the telegraphing of pictures. In one way of accomplishing this the picture to be transmited, which may be transparent or non-transparent, is fixed at the sendingstation on a cylindrical surface and scanned over with a point beam of light in the form of a spiral, the light projected through or reflected from saidpicture being caught by a photoelectric cell which thereby generates electric pulsations. The latter are transmitted by wire to the receiving station there to be applied to the grid of a receiving station for the purpose of modulating the intensity of a beam of ions. This beam of ions is received on an insulated surface mounted on a drum which is rotated in synchronism with the corresponding device at the sending station. The electrogram thus produced can then be developed and, if desired, copied by photographic methods.

Various methods can be employed for fixing the electrograms, after development by the methods outlined previously. The electrograms can be sprayed with white shellac or a lacquer and the solvent evaporated. It is also possible to imbed the powder particles into the film by pressing with a roller, for example. On the other hand the receiving surface may be made of low melting material such as parafiin and this may" be heated to the point at which the electroscopic powder sticks to the surface after cooling. Or the receiving surface may be made of a material, such as acetyl cellulose, capable of softening upon application of a solvent such as acetone, the powdered image being sprayed with this solvent thereby causing the powder to adhere.

I have found that a paper impregnated or coated with parafline is particularly suitable for use as receiving surface.

It is not believed necessary to further elaborate upon the various methods of employing electrography in detecting, indicating, measuring and recording various conditions. Other methods within the scope of the following claims and therefore within the preview of my invention will be immediately evident to those skilled in the art.

What I claim is:

1. In an apparatus for producing images in combination, means for generating a beam of gaseous ions, a receiving surface of insulating material intercepting said beam of ions, 9. diaphragm formed with an opening through which said beam can pass towards said receiving surface, means for generating an electric field having lines of force extending through said opening including electrically charged conductive means affecting the travel of said beam of gaseous ions from said first means to said receiving surface, and mechanicalmeans for maintaining the source of said beam and said receiving surface in relative motion.

2. In an apparatus for producing images in combination, a source of gaseous ions, means for producing a beam of said ions, an insulating surface, a conductive diaphragm arranged between said source of gaseous ions and said insulating surface and possessing an opening for the passage of said beam, an electric field having lines of force extending through said opening to a conductive surface adjacent to said insulating surface, means for controlling the intensity of said beam, and mechanical means for maintaining the source of said beam and said receiving surface in relative motion.

3. The apparatus of claim 1, wherein the receiving surface has the form of an endless belt.

4. In an apparatus for producing images in combination, means for generating a beam of gaseous ions, means for applying a varying potential to the control of the intensity ofsaid beam of ions, a diaphragm having an opening for the passage of said beam of ions, electrical means for directing said controlled beam of ions through said opening of the diaphragm against a moving insulating surface, to thereby produce a latent image and means for rendering said latent image visible.

5. In an apparatus for producing images in combination, means for generating a beam of 1| gaseous ions, means for applying potentials varying in accordance with the variations of said images to said beam for controlling the intensity thereof in a manner corresponding to said potentials, a diaphragm having an opening for the passage of said beam of ions, electrical means for directing said'controlled beam through said opening against a moving insulating screen to produce latent images on said screen and means for rendering visible the latent images.

6. An apparatus comprising in combination, a source of gaseous ions, a conductor adapted, when electrically charged, to attract a beam of said gaseous ions, an insulating receiving surface adjacent said conductor intercepting the beam of ions attracted by said conductor, a second conductor having an opening intermediate said source of ions and said receiving surface adapted, when electrically charged, to control the passage of ions from said source through said opening to said receiving surface, electric connections between said source of ions and said conductors for electrically charging said conductors, and

mechanical means for producing relative motion between said beam of ions and said receiving surface.

7. The method of producing images by means of electrostatic charges which comprises pro ducing a beam of gaseous ions, directing the beam towards a conductive surface displaced therefrom, controlling the intensity of said beam in accordance with varying conditions, intercepting the travel of said beam upon a relatively moving support capable of storing the electrostatic charges of the ions of the beam thereupon, and treating the latent images thus produced with an electroscopic powder.

8. The method of producing images by means of electrostatic charges which comprises producing a beam of gaseous ions, directing the beam towards a conductive surface displaced therefrom, controlling the intensity of said beam in accordance with varying conditions, and intercepting the travel of said beam upon a relatively moving support capable of storing the electrostatic charges of the ions of the beam thereupon.

9. The method of producing images by means of electrostatic charges which comprises producing a beam of gaseous ions, directing the beam towards a conductive surface displaced therefrom, confining the extent of said beam with an electrically charged slotted member, controlling the intensity of said beam in accordance with varying conditions, andintercepting the travel of said beam upon a relatively moving support capable of storing the electrostatic charges of the ions of the beam thereupon.

10. The method of producing images by means of electrostatic charges which comprises producing a beam of gaseous ions at a gaseous pressure within the range of about 0.001 mm. of mercury to atmospheric pressure, directing said beam towards a conductive surface displaced therefrom, controlling the intensity of said beam in accordance with varying conditions intercepting the travel of said beam upon an insulating surface, and producing relative motion between said surface and said beam.

11. The method of producing images by means of electrostatic charges which comprises producing a beam of gaseous ions, directing the beam towards a conductive surface displaced therefrom, controlling the intensity of said beam by varying the electrical potential of said conductive surface in accordance with said varying conditions, intercepting the travel of said beam upon an insulating surface, and producing relative movement between said beam and said surface.

12. The method of producing images by means of electrostatic charges which comprises producing a beam of gaseous ions, directing the beam towards a conductive surface displaced therefrom, confining the extent of said beam with an electrically charged slotted member, controlling the intensity of said beam by varying the electric potential of said slotted member in accordance with said varying conditions, and intercepting the travel of said beam upon a relatively moving support capable of storing the electrostatic charges of the ions of the beam thereupon.

PAUL 5mm. 

